In the consumer sector in particular, there is an increasing demand for economical acceleration sensors for all three spatial directions having a small configuration and the lowest possible energy consumption.
Gang Li et al., “Design and fabrication of a highly symmetrical capacitive triaxial accelerometer,” Journal of Micromechanics and Microengineering 11 (2001) 48-54, describe a micromechanical sensor element of the kind cited initially with which accelerations in all three spatial directions can be sensed. The known sensor element encompasses a seismic mass of truncated pyramidal shape, having a square base surface, which is suspended in a frame via four struts so that it is deflectable in all three spatial dimensions. The seismic mass is patterned out of a semiconductor substrate, while the four struts are configured only in a surface layer of this substrate. As a result of corresponding doping, this surface layer functions as an electrode. The configuration of the known sensor element further encompasses a rigid glass wafer that spans across the suspension struts and the seismic mass but is disposed at a distance from the doped substrate surface. The surface of the glass wafer facing toward the doped substrate surface is equipped with multiple counterelectrodes. The individual directional components of an acceleration acting on the seismic mass are ascertained here by evaluating the capacitances that are sensed between the substrate-side electrode and the individual glass-wafer-side counterelectrodes.
The above-discussed sensor element thus encompasses a seismic mass having only one movable electrode but multiple stationary counterelectrodes disposed at a distance from one another on a glass wafer, so that multiple electrode pairs are available for capacitive signal sensing.
Manufacture of the this sensor element is comparatively complex, since the glass wafer and the semiconductor substrate must be processed independently of one another, and then joined to one another in aligned fashion. In addition, the semiconductor substrate must be processed on two sides. Patterning of the back side, in particular, in order to disengage the seismic mass, requires special method steps. In addition, the space requirement of a component structure produced using bulk micromechanics is relatively large.